Recent radio communication systems adopt a scheme for performing packet switching on a radio access interface such as Code Division Multiple Access (CDMA) and Orthogonal Frequency Division Multiplexing (OFDM) in order to flexibly support diversified services, increase compatibility with the Internet, and further to increase frequency use efficiency. High-speed Downlink Packet Access (HSDPA) standardized in 3GPP and 802.16 (WiMax) standardized in IEEE are the typical examples.
In these systems, a base station apparatus selects a user (or a plurality of users) to which a packet is to be sent next, that is, in a next frame using a common radio channel in consideration of a radio state (to be referred to as Channel Quality Indicator(CQI) hereinafter), Quality of Service (QoS), and buffer residence amount and the like of each user (mobile station apparatus). This operation is generally called packet scheduling.
For example, in HSDPA, user data (user packet) is transmitted in a time division multiplex manner on a High-speed Physical Downlink Shared Channel (HS-PDSCH) that is a common channel. HS-PDSCH is divided to frames of 2 ms, and the base station apparatus selects a user for transmitting data for each frame and transmits the data.
More particularly, for example, the base station apparatus can select a user having good CQI (Max C/I algorithm), and can select a user of good CQI (Max C/I algorithm), and can select a user in which an instantaneous value of CQI (instantaneous CQI) is relatively greater than an average value (average CQI) of CQI (Proportional Fairness(PF) algorithm). HS-PDSCH is a channel in which data of various users are time-division multiplexed, and sports high speed transmission speed of several Mb/s. Therefore, there are much wastes if all mobile station apparatuses continuously receive the HS-PDSCH. Thus, in HSDPA, the base station apparatus signals presence or absence of data on the HS-PDSCH to the mobile station apparatus using High-speed Shared Control Channel (HS-SCCH). The mobile station apparatus continuously receives HS-SCCH, and when receiving signaling indicating there is data addressed to the own apparatus, the mobile station apparatus receives HS-PDSCH.
For example, as shown on FIG. 1, in a frame at the left end, the base station apparatus signals that there is data addressed to user 1 using HS-SCCH 1, so that the user 1 receives the HS-SCCH 1, and the user 1 receives HS-PDSCH 1-5 at a next timing.
In addition, in the next frame, the base station apparatus performs signaling using HS-SCCH 1 and HS-SCCH 2 informing that there is data addressed to the user 1 and the user 2, so that the user 1 and the user 2 respectively receive HS-SCCH 1-3 and HS-SCCH 4-6 in a second frame.
By the way, a plurality of HS-PDSCHes, for example, 10 HS-PDSCHes can be established simultaneously in a same cell (sector), and it is also possible to transmit data of a single user using a same frame over a plurality of HS-PDSCHes. Also in this case, the specification is defined such that signaling can be performed for the mobile station apparatus using a single HS-SCCH.
In addition, in HSDPA, simultaneous transmission to a plurality of users is available using a plurality of HS-PDSCHes. In this case, since it is necessary to perform signaling for a plurality of mobile station apparatuses that are scheduled simultaneously, the corresponding number of HS-SCCHes are necessary. For supporting such operation form, HSDPA is specified such that the mobile station apparatus continuously receive four HS-SCCHes.
In the following, a common channel corresponding to HS-PDSCH is called SCH, and a channel corresponding to HS-SCCH is called CCH.
Here, load of a mobile station apparatus can be considerably decreased by continuously receiving a CCH, when compared with continuously receiving SCH. However, there is its receiving load so that battery is consumed. Especially, in a service in which data arrives discontinuously like web browsing, the battery is rapidly consumed if HS-SCCH is continuously monitored for a long time even though there is no data when a web page is being browsed.
The battery can be saved by once releasing a connection until data arrives, for example, until opening a next web page and entering into a waiting mode. But, according to this method, it is necessary to perform re-connection processes when data arrives so that service response is lowered.
To avoid such problem, CCH can be received discontinuously (Discontinuous Reception(DRX)). A mobile station apparatus under DRX receives CCH in a cycle (DRX cycle) (to be referred to as DRX opportunity hereinafter), and the mobile station apparatus does not receive CCH in the remaining time. By performing DRX, battery consumption due to continuously receiving CCH can be avoided.
For example, when there is no data addressed to the own mobile station apparatus for a predetermined time, the mobile station apparatus can autonomously control itself to automatically perform DRX for CCH. In addition, for example, the mobile station apparatus negotiates with a base station apparatus or a network to control itself to perform DRX for CCH.
When the mobile station apparatus performs autonomously control for DRX, the base station apparatus can determine DRX states of the mobile station apparatus by applying a similar rule. For example, in 802.16, when there is no scheduled data at a DRX opportunity, operation for doubling the DRX cycle is repeated so that further battery saving is performed by increasing the DRX cycle.
A mobile station that is once signaled that there is data using CCH at a DRX opportunity can immediately stop DRX to return to a state of CCH continuous reception. In addition, in this case, the mobile station apparatus can perform control to decrease the DRX cycle.
In addition, in a cellular system, the mobile station apparatus performs handover processes to switch base station apparatuses for connection when the user moves. For example, in a WCDMA system, the mobile station apparatus measures signals of surrounding base station apparatuses, and when a specific condition is satisfied, that is, when receiving levels are switched, for example, the handover processes are performed. Here, a WCDMA mobile station apparatus that has only one receiver cannot measure a signal having a different frequency while performing communications.
Thus, by launching a compressed mode (temporarily doubling the transmission rate to temporally compress transmission so as to generate a gap in a transmission time, that is, Discontinuous Transmission(DTX)), a gap is generated in a reception time (that is, DRX) so that the different frequency is measured in that time.
In the same way, different frequency is measured by performing DRX in HSDPA in which WCDMA is expanded to a packet switching scheme, so that the base station apparatus cannot transmit a packet to the user during the time (or, even though it sends a packet, the mobile station apparatus cannot receive the packet so that it becomes waste). This similarly applies to a case for measuring a radio wave of a different radio system. That is, when different frequency or different system are tried to be measured, it becomes necessary to perform DRX, and the base station apparatus cannot transmit data during the time.